1. Field of the Invention
The present invention relates to a magnetoresistive head with an oversized free layer for thermal and magnetic stability.
2. Description of the Related Art
In a conventional head, a spacer between a free layer and a pinned layer is non-magnetic (comprising either a conductive layer in the case of GMR, or an insulator in the case of tunneling TMR). Therefore the magnetic flux of the media (media flux) will change the magnetization direction of the free layer only. The magnetization of the pinned layer is fixed and not being affected by the media flux.
In a ballistic magneto resistive head (hereinafter BMR head) of the present invention, a higher MR ratio can be achieved compared to giant magneto resistive (GMR) or tunneling magnetoresistive (TMR) cases.
As disclosed in G. Tatara et. al., Phys. Review Letters, Vol.83, the origin of BMR results from an additional resistance of a magnetic domain wall in a nano-contact between two ferromagnetic layers or wires. The magnetic domain wall is created when the magnetization in these two ferromagnetic layers are anti-parallel. The size of the magnetic domain wall is in the nanometer scale, the scattering of electron is strong.
The BMR value depends on the magnetic domain wall configuration and the scattering of electron when the electron passes through the magnetic domain wall in the nano-contact region. For the application of BMR to a read head it is important to guarantee the stability of the nano-contact against an external field. Its magnetic configuration should be determined only by the change in the free layer magnetization direction.